James Hansen read the first draft and wrote me back, “Very important for the public to understand this — why has nobody articulated this already?” I don’t know the answer. All I can say is that while I was writing the article, the central point dawned on me:

The more I write about global warming, the more I realize I share some things in common with the doubters and deniers who populate the blogosphere and the conservative movement. Like them, I am dubious about the process used by the U.N. Intergovernmental Panel on Climate Change (IPCC) to write its reports. Like them, I am skeptical of the so-called consensus on climate science as reflected in the IPCC reports. Like them, I disagree with people who say “the science is settled.” But that’s where the agreement ends.

The science isn’t settled — it’s unsettling, and getting more so every year as the scientific community learns more about the catastrophic consequences of uncontrolled greenhouse gas emissions.

The big difference I have with the doubters is that they believe the IPCC reports seriously overstate the impact of human emissions on the climate — whereas the actual observed climate data clearly show they dramatically understate the impact.

I point out many instances of this in the article. For instance, “The recent [Arctic] sea-ice retreat (PDF) is larger than in any of the (19) IPCC [climate] models” — and that was a Norwegian expert in 2005. Since then, the Arctic retreat has stunned scientists by accelerating, losing an area equal to Texas and California just last summer.

I also discuss the fact that “the scientific community, the progressive community, environmentalists and media are making a serious mistake by using the word ‘consensus’ to describe the shared understanding scientists have about the ever-worsening impacts that human-caused greenhouse-gas emissions are having on this planet.” Part of the reason is that “When scientists and others say there is a consensus, many if not most people probably hear ‘consensus of opinion,'” whereas, as I explain, “science doesn’t work by consensus of opinion. Science is in many respects the exact opposite of decision by consensus.“

Another reason is that the IPCC “consensus” clearly understates what we face from uncontrolled greenhouse-gas emissions. As the article concludes:

Why are recent observations on the high side of model projections? First, as noted, most climate models used by the IPCC omit key amplifying feedbacks in the carbon cycle. Second, it was widely thought that increased human carbon dioxide emissions would be partly offset by more trees and other vegetation. But increases in droughts and wildfires — both predicted by global warming theory — seem to have negated that. Third, the ocean — one of the largest sinks for carbon dioxide — seems to be saturating decades earlier than the models had projected.

The result, as a number of studies have shown, is that the sensitivity of the world’s climate to human emissions of greenhouse gases is no doubt much higher than the sensitivity used in most IPCC models. NASA’s Hansen argued in a paper last year that the climate ultimately has twice the sensitivity used in IPCC models.

The bottom line is that recent observations and research make clear the planet almost certainly faces a greater and more imminent threat than is laid out in the IPCC reports. That’s why climate scientists are so desperate. That’s why they keep begging for immediate action. And that’s why the “consensus on global warming” is a phrase that should be forever retired from the climate debate.

The article is long, so my final paragraph was cut:

I do believe in science. And I do believe in real-world observations. Perhaps the central question of our time is whether those who don’t will stop those who do from saving the planet.

I’ll make the final sentence the basis of a future article.

For now, I’ll try to follow my own advice and stop using the word consensus …